Carotenoids are yellow, red and orange pigments that are widely distributed in nature. Although specific carotenoids have been identified in various fruits and vegetables, bird feathers, egg-yolk, poultry skin, crustaceans and macular eye region, they are especially abundant in marigold petals, corn and leafy vegetables. The correlation between dietary carotenoids and carotenoids found in human serum and plasma indicate that only selected groups of carotenoids make their way into the human blood stream to exert their effect.
Carotenoids absorb light in the 400-500 nm region of the visible spectrum. This physical characteristic imparts the yellow/red color to the pigments. Carotenoids contain a conjugated backbone composed of isoprene units, which are usually inverted at the center of the molecule, imparting symmetry. Changes in geometrical configuration about the double bonds result in the existence of many cis- and trans-isomers. Mammalian species do not synthesize carotenoids and therefore these have to be obtained from dietary sources such as fruits, vegetables and egg yolks. In the recent years, carotenoids have been attributed several health benefits, which include prevention and or protection against serious health disorders.
Carotenoids are non-polar compounds classified into two sub-classes, namely more polar compounds called xanthophylls or oxy-carotenoids and non-polar hydrocarbon carotenes like [beta]-carotene, lycopene, etc. Both the sub-classes have at least nine conjugated double bonds responsible for the characteristic color of the carotenoids. Xanthophylls have ring structures at the end of the conjugated double bond chain with polar functionalities, such as hydroxyl or keto groups. Examples of xanthophylls include lutein, zeaxanthin, capsanthin, canthaxanthin, β-cryptoxanthin, astaxanthin, etc. As natural colorants and also for their role in human health, xanthophylls containing lutein and zeaxanthin have attracted the renewed attention of scientists and researchers in the biomedical, chemical and nutritional field in recent years.
Lutein and zeaxanthin contribute to yellow and orange-yellow color respectively. Lutein and zeaxanthin can be present in plant material in free form (non-esterified) and also as esters. Lutein is present in green leafy vegetables like spinach, kale and broccoli in the free form while fruits like mango, orange, papaya, red paprika, algae and yellow corn. These sources generally contain lutein in the form of its esters etc. Lutein is also present in the blood stream and various tissues in human body and particularly the macula, lens and retina of the eye.
Essentially, lutein esters and lutein in the free form are commercially important nutraceuticals obtained from marigold flowers. In the fresh marigold flowers, lutein esters exist in trans-isomeric form, whereas exposure to heat, light, oxygen, acid, etc. catalyses isomerization from trans- to cis-lutein geometric isomeric forms. As a nutraceutical and trod additive, the trans-isomeric form of lutein is preferred because of better bio-availability and deeper yellow color compared to the corresponding cis-isomeric form.
Various carotenoids are present in human plasma, but only the xanthophylls lutein and zeaxanthin are found in the retina in considerable amount, with particularly high levels in the macula lutea, the yellow spot in the center of the fovea. Degeneration of the retina and retinal pigment epithelium in the region of the macula lutea leads to eye diseases, such as age-related macular degeneration (AMD). Lutein and zeaxanthin are the predominant carotenoids in the human macula lutea. Epidemiological data suggest that an increased intake of diet enriched in lutein can diminish the risk of MAD and associated or related diseases.
Therefore, a need exists for the increased uptake of xanthophylls such as lutein and/or zeaxanthin in human plasma, and especially in the macula lutea.